SCUBA Polarization Measurements of the Magnetic Field Strengths in the L183, L1544, and L43 Prestellar Cores

By R. Crutcher, D. Nutter, D. Ward-Thompson, J. Kirk. 2003

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We have mapped linearly polarized dust emission from L183 with the James Clerk Maxwell Telescope SCUBA polarimeter and have analyzed these and our previously published data for the prestellar cores L183, L1544, and L43, in order to estimate magnetic field strengths in the plane of the sky, Bpos. The analysis used the Chandrasekhar-Fermi technique, which relates the dispersion in polarization position angles to Bpos. We have used these estimates of the field strengths (neglecting the unmeasured line-of-sight component) to find the mass-to-magnetic flux ratios λ (in units of the critical ratio for magnetic support). Results are Bpos ≈ 80 μG and λ ≈ 2.6 for L183, Bpos ≈ 140 μG and λ ≈ 2.3 for L1544, and Bpos ≈ 160 μG and λ ≈ 1.9 for L43. Hence, without correction for geometrical biases, for all three cores the mass-to-flux ratios are supercritical by a factor of ~2, and magnetic support cannot prevent collapse. However, a statistical mean correction for geometrical bias may be up to a factor of 3; this correction would reduce the individual λ's to λcor ≈ 0.9, 0.8, and 0.6, respectively; these values are approximately critical or slightly subcritical. These data are consistent with models of star formation driven by ambipolar diffusion in a weakly turbulent medium but cannot rule out models of star formation driven by turbulence.

Subfields: Astronomy and Astrophysics, Instrumentation, Statistical and Nonlinear Physics

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Citations in the corpus

Magnetic processes in a collapsing dense core I. Accretion and ejection (2007, unknown): “It is worth stressing that such values of µ in the range 5 − 2 are compatible with the more pessimistic estimates derived from measurements of the magnetic intensity in the dense cores (Crutcher 1999, Crutcher & Troland 2000, Crutcher et al. 2004).”
Probing the Evolutionary Status of Starless Cores through N2H+ and N2D+ Observations (2004, background): “Core shape could, for example, reflect the magnetic field structure, and indeed several of the cores in our sample show linear polarization of around 5%–10% (e.g., Crutcher et al. 2004), suggesting magnetic fields of order 100 G.”
Simulating the Formation of Molecular Clouds. I. Slow Formation by Gravitational Collapse from Static Initial Conditions (2006, background): “For a gas cloud in which all of the hydrogen is already fully molecular, Crutcher et al. (2004) show that the mass-toflux ratio of the cloud can be written in units of this critical value as λ ≡ (M/Φ) (M/Φ)crit = 7.6 × 10−21NH2 B , (48) where NH2 is the H2 column density of the cloud in units of cm…”
Simulating the Formation of Molecular Clouds. II. Rapid Formation from Turbulent Initial Conditions (2006, background): “Observations of magnetic field strengths inmolecular cloud cores, summarized in Crutcher (1999) and Crutcher et al. (2004), find a smaller mean value, (M / )mean ’ 2, but there is significant scatter around this value, and in any case it is far from clear that we would expect to find the same value…”
Cold Dark Clouds: The Initial Conditions for Star Formation (2007, background): “For cores L1544, L183, and L43, Ward-Thompson et al. (2000) and Crutcher et al. (2004) have found polarization vectors that are fairly uniform but not aligned with the minor axis of the cores by about 30◦, as it would have been expected by ambipolar diffusion models (but see Basu 2000 for an…”
The initial conditions of isolated star formation — VI. SCUBA mapping of pre-stellar cores (2005, background): “…et al. 2000) that turbulent models which include magnetic fields can only reproduce polarisation maps of prestellar cores if they are in the regime where the turbulent and magnetic energies are roughly equal (e.g. Ostriker, Gammie & Stone 1999; Ostriker, Stone & Gammie 2001; Crutcher et al. 2004).”
Planck intermediate results: XXXV. Probing the role of the magnetic field in the formation of structure in molecular clouds (2015, unknown): “Stability can be assessed using where N mftH 2 and B mft are the H 2 column density and magnetic ﬁeld strength along a magnetic ﬂux tube (Crutcher et al. 2004).”
Tracing Magnetic Fields with Aligned Grains (2007, background): “Indeed, the properties of these cores summarized in Ward-Thompson et al. (2002) and Crutcher et al. (2004) fit into the category of zones that, according to LGM97, should not contain aligned grains.”
The James Clerk Maxwell Telescope Legacy Survey of Nearby Star‐forming Regions in the Gould Belt (2007, methodology): “Polarized dust emission is detected from objects on all measured scales (e.g., Matthews et al. 2001; Crutcher et al. 2004) and from compact cores, regardless of evolutionary epoch (e.g., Ward-Thompson et al. 2000; Matthews & Wilson 2002), as illustrated in Figure 16.”
Radiative torque alignment: essential physical processes (2007, background): “However, Crutcher et al. (2004) pointed out that polarization data do not sample the innermost core regions3, and this provides an explanation for polarization “holes” (see Matthews & Wilson 2000, 2002; Matthews et al. 2001; Lai et al. 2002).”
THE LEGACY OF SCUPOL: 850 μm IMAGING POLARIMETRY FROM 1997 TO 2005 (2009, unknown): “The efforts of J. Greaves, A. Chrysostomou G. Schieven, J. Kirk, D. Ward-Thompson, R. Redman, P. Bastien, and F. Poidevin in consulting observing logs and data reduction records are appreciated.”